Finishing of artificial leather



P 1935, M. o. SCHUR ET AL I FINISHING OF ARTIFICIAL LEATHER Filed Jan..27, 1955 75 dizakw er/gaze (7&dd

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Patented Sept. 24, 1935 UNITED STATES FINISHING 0F ARTIFICIAL LEATHERMilton 0. Schur and Benjamin G. Hoos, Berlin, N. 11., assignors to BrownCompany, Berlin, N. H., a corporation of Maine Application January 27,1933, Serial no. 653,854

14 Claims.

This invention relates to the manufacture of artificial leathers moreparticularly of the kind comprising a base of interfelted cellulosefibers bonded together with rubber as an impregnating Artificial leatherof this general class is customarily made by forming a bibulous,waterlaid web or felt on machinery of the papermaking type, impregnatingthe dry web with a suitable latex composition, and drying theimpregnated web so as to coagulate the rubber bonding agent, whichimparts to the dried product, toughness, tear-resistance,water-repellency, body, and other leatherlike qualities. In someinstances, the rubber may be coagulated in the freshly-impregnated webthrough the use of suitable coagulating media, such as acetic acid,alum, or the like, as this does away with the tendency for thedispersed'rubber particles to migrate to the surface of the web duringthe drying operation.- It is usually preferable to put the rubberimpregnant introduced into the web in a vulcanized condition, as byusing a vulcanized latex composition to begin with and/or by addingvulcanizing ingredients to .the latexcomposition and then drying thelateximpregnated web under vulcanizing temperature conditions;

Before artificial leather fabricated as just describedis useful in manyarts, it must be finished to simulate very closely calf-skin, kidskin,or other similar soft or pliant natural leathers treated with a,so-called water finish. While this desideratum applies to artificialleathers to serve, for instance, in note book covers, cigarette cases,belts, automobile tops, or the like, it also obtains in connection withartificial leathers which are used for upholstering furniture,automobile seats, or the like, and as shoe upper material. In theselatter connections, moreover, the artificial leather must be finished insuch a way as to undergo satisfactory tacking, stitching, or similaranchorage and, above all, to resist effectively abrasion and flexingincident to such service.

So far as we are aware, no one has hitherto prepared an artificialleather intended to simulate calf-skin, kid-skin, or other similargenuine smooth leathers and which has successfully been used on acommercial scale as upper stock in the manufacture of shoes. Thedifiiculties have been many, not the least of which is the difficulty offinishing smooth surface artificial leather to answer the requirementsof the trade, because blemishes, minute and otherwise, present in theartificial leather base would show up. disconcertingly plainly in asmooth surface resembling the finished skin side of such naturalleathers as calf-skin, kid-skin, or the like. Indeed, water-finishedartificial leathers, as heretofore made, either had the coarse, hungry 8look of split leather, or, if coated sufficiently heavily to fill thesurface pores, were apt to resemble oil cloth more nearly than naturalleather, because of the absence therefrom of pores and other surfacemarkings such as occur in natural leather and lend a characteristicappearance thereto. The fact is that when artificial v leather is sofinished as to cover up the surface blemishes inhering in an artificialleather comprising even the best-textured and smoothest faced feltedbase, several serious difllculties immediately crop up. Thus, thefinished surface rather than being leatherlike in appearance and inproperties is, as already indicated, reminiscent of oil cloth, developsa coarse break and 20 becomes permanently and unsightly wrinkled uponflexing, and is apt to be practically impervious to the passage ofperspiration therethrough, i. e., to lack breathing qualities, withconsequent "burning of the feet when used as 35 a shoe upper material.This holds true when the finishing composition contains any one or V amixture of such materials as rubber, lacquer, wax, resin, casein, oroxidizable oil. When it is attempted to lend grain to the artificialleather 30 by embossing, it is found exceedingly diificult, if notpractically impossible, to realize a grain sufficiently characteristicof natural leather.

In accordance with the present invention, we produce an artificialleather which is so fin-35 ished that not only is it highly satisfactoryfor the various purposes hereinbefore enumerated, but is eminentlysuited for the exacting role of a shoe upper material. It is in thislatter role, v therefore, that we shall now describe our fin- 4o ishedartificial leather. In producing our finished artificial leather, werecognize that a skin is necessary not only to disguise or to cover therelatively coarse grain of the base sheet,

a but also to protect the sheet against abrasion 45 suffered duringshoe-making as well as against scufiing encountered during service. Wetherefore provide our base sheet with a skin sufficiently tough towithstand to a reasonable degree abrasion and scufiing,-yet not so thick50 that unsightly breaking and creasing occurs as a result of flexing.In addition, the skin is sufliciently elastic to remain intactthroughout molding or lasting and sufliciently tough andabrasion-resistant to withstand the severe wip- 56 Q '10 were afragmentscuffed up and an attempt,

made to pick it up, an entireor large area of skin would be removed fromthe base sheet. It is capable of undergoing continued flexing as at thevamp portion of a shoe without crack- 15 ing or serious wrinkling. Allof the foregoing properties are exceedingly important, as failure torealize any one of them means the failure of a shoe upper stock from a.commercial point of view.

After long-continued investigation and research, we have found that askin-forming com-' position wherein glue, glycerine, and latex, are'combined in definite proportions can be applied to a base sheet ofartificial leather in controlled 25. amount to yield a primary skin ormembrane posessing many of the foregoing desiderata. Each of thecomponents of the skin-forming composition contributes mostsignificantly to the properties desired in the skin deposited on the30.--base sheet. Thus, the rubber afiorded by the [latex impartselasticity to the skin. The glue furnishes the desired resistance toabrading or scufilng action. The glycerine functions not only as aplasticizing or flexibilizing agent for the 35 glue, but increases thecapacity of the skin-for permitting moisture and perspiration to diffusetherethrough and thus to minimize the danger of the leather burning thefeet. If excessive glue is used, the skin becomes brittle 40 and cracksduring flexing an'd/or stretching. If

excessive glycerine is used to compensate for such defect, the skinbecomes sticky and cannot be finished to look like leather. If excessiverubber is used, the skin falls to adhere properly to 45 the base, sothat, when the skin is scuffed up in use and a protruding fragment ispicked at, the skin will peel over a substantial area. When theskin-forming composition is properly compounded, however, a fragment ofskin will, when so, picked at, break oif in much the same way' that "theskin on natural leather does.

.We shall now give a typical primary skinforming composition fallingwithin the purview of the present invention. Here is the formula 55 sucha compo'fltionr- Per cent Latex solids added as in the form of normallatex containing about 30% to 40% latex solids 60 to 80 00--Anti-oxidant as in the form of {Age- Rite White", about 0.36

Dye or. pigment such as "Con. Pheno 8G about 1.33 Animal glue solids 10to 25 Glycerine as in the form of anhydrous commercial gLvcerine 7 to 15'The foregoingskin-f'orming composition may be applied to the surface ofthe artificial leather 7o Qas a dilute aqueous mixture having a watercontent of say, about 82%, when application is made by the usualatomizer or spray gun. While the composition may be applied by the useof the usual coating or spreading machines as one or is -more layers, itis preferable to spray the composition onto the surface of theartificial leather as four successive coats with partial drying of onecoat before a succeeding coat is superimposed. In any case, however, thethickness of the deposited skin is closely regulated so that in drycondition it weighs from about 6 to 18 grams per square foot ofartificial leather surface. When the composition is applied by aspreading machine, it may be of a creamy 'or thicker consistency so asto facilitate spreading. If desired, suitable thickening agents, such asthe alginates, may be added in small amount to the composition topromote easy-spreading thereof.

While there are various sequences of preparing the primary skin-formingcomposition, we prefer to dissolve the dye and the glue as a mixture ina sniall amount of warm water and to add the dissolved anixture slowlyand with constant gentle stirring to a previously prepared 20 aqueousmixture containing the .latex, anti-oxidant, and glycerine inappropriate amount and diluted with sufllcient water to yield acomposition amenable to successful spraying. In order that the sprayedcomposition may dry into the smoothest kind of skin, it is preferablethat drying of the sprayed composition be accomplished slowly at aboutroom temperature.

'After a primary skin has been deposited and dried as hereinbeforedescribed on the base sheet of artificial leather, it is surfaced with afilm of a glue-glycerine mixture. The mixture may consist of about 30%to 60% of commercial anhydrous glycerine and 70% to 40% of animal glue.

a typically good mixture consisting of 55% glycer- 35 to the solution soas to impart the desired color thereto. The dried film, by virtue of theflexibilizing action of the glycerine on the glue, resembles closely theprotein skin of natural leather and becomes integrated with theunderlying primary skin. For the best results, the film when 1 driedshould add from 0.05 to 0.50 grams to each square foot of the artificialleather. It is thus seen that the surfacing film is very much thinnerthan the underlying skin. The surfacing film may be dressed with amixture of shellac, ox-

blood, glue and glycerine, or any other suitable water finish which maybe conveniently applied with a swab. The water finish may serve to adddepth, gloss, feel, and other artistic qualities to the artificialleather and may in some instances w I include dyes and/or p miehts.

It is distinctly desirable to insolubilize or to tan the glue componentof the skin as a whole, including that of the surface film. Whilevarious insolubilizing or tanning agents may be used for 55 thispurpose, it is preferable to expose, the finished sheet to the action offormaldehyde under the appropriate time, concentration and temperatureconditions. One satisfactory procedure is to expose the flnished sheetto an'atmosphere of formaldehyde vapor atv room temperature for about 16hours and then to heat the sheet to a temperature of about 220 to 230?F. in the air and to the sheet at this temperature for about IOminutesor so. The final heating'operar V tannic acid, the usual tanningextracts and, un-.

der carefully controlled conditions, through the use of chromates andultra-violet light.

Our practice of finishing artificial leather is comparativelyinexpensive and surprisingly effective. The primary skin has remarkablyhigh scuff resistance and tenacity of bond with the base sheet ofartificial leather. The primary skin cannot, however, be successfullyglazed because of its high rubber content. As is wellknown, leather isglazed or burnished by frictioning it with smooth, hard objects, usuallyby bringing a curved glass surface to bear against its surface andreciprocating the curved glass surface thereagainst until the desiredgloss is reached. The rubber component of the primary skin preventssmooth sliding action of the glass surface thereupon and tends to becomeso heated as to stick to the glass surface and thus to inhibit smoothburnishing' action. It is for this reason and also because the primaryskin is comparatively easily scratched and defaced by the digging-inaction of the wipers of a bed-lasting machine, that we surface and dressthe primary skin with films which are highly resistant to scratching andwhich makes possible satisfactory glazing and staking of the artificialleather. The films amalgamate intimately with the primary skin so as toconstitute in effect a single skin which possesses the desired combinedproperties of both the primary skin and surface film. In order todemonstrate the scufi resistance of artificial leathers finished inaccordance with our invention, samples were rubbed on the finishedsurface against a coarse canvas pad as shown in Figures 1, 2, and 2a,wherein,---

Figure 1 is a side view of the testing machine.

Figure 2 is a section on the line 2-4 of Figure 1.

Figure 2a. is an enlarged view of a member of the machine.

As shown in Figures 1 and 2, a can i provided with shot 2 is mounted onthe carriage] supported by the curved member 4 to which is clamped thespecimen of leather 5, finished. side down, resting on the canvas 6fastened to the hardwood base bymeans of thumb-tacks. The dimension p is1 inch; the radius of curvature r is inches.

' The total weight carried by the specimen is 600 Wet canvas Dry canvasNatural kid-skin 5 to 12 minutes 5 to 12 minutes. Natural calf-skin 5 to20 minutes... to 20 minutes. Our artificial leather 5+ minutes 5 to 20minutes.

I The natural leathers used for purposes of comparison were of the usualcommercial variety weighted 3 and were finished in the conventionalmanner. The values tabulated above represent the time required to rub upfibers on the specimens listed. It is to be observed that the scufi.resistance of our finished artificial leather approaches that of 5 theusual commercial natural upper leathers. The remarkable thing aboutour-finished artificial leather is that this scuif resistance isrealized in combination with the equally important surface qualitieshereinbefore mentioned, including elasticity, flexibility, hardness,scratch resistance, and an appearance simulating that of naturalleather.

It is important that theglycerine remain in the skin. We have found thatwhile a tough, 15 flexible film may initially be laid down on theartificial leather, nevertheless the glycerine tends to migrate into thebase sheet, thereby rendering the film, so to speak, unstable, for, asthe percentage of glycerine in the film is reduced, the film becomesless elastic and is apt to crack easily under'the stresses of continuedflexing. We have found that if the base sheet contains the properquantity of glycerine, the skin is rendered comparatively stable,because the tendency for migration of glycerine is greatly reduced, andthe elasticity of the film is greatly enhanced.

While the artificial leather base, which is finished in accordance withour invention, may be made in many ways from various kinds of fibrousfoundations, including woven as well as felted webs of fiber, andvarious rubber-impregnating compositions, including rubber solutions aswell as rubber dispersions, such as latex, we prefer to start with a webor felt of unbleached purified 85 wood pulp and to impregnate the webwith a vulcanized latex composition compounded withglycerine, additionalvulcanizing agents, and a. suitable anti-oxidant, such as Age-RiteWhite, as disclosed in application Serial No. 575,164, 40 filed November14, 1931 by Milton 0. Schur. As described in that application, a soft,fiuify web composed of substantially unbeaten, interfelted wood pulpfibers having an alpha cellulose con tent of at least about 93% may bepassed progressively as a sheet of indefinite length through a bath ofthe prevulcanized and compounded latex composition, thence throughsqueeze rolls, and finally through a hot-air drier maintained at about170 at its inlet end and at about 220 F. at its exit end. Drying of theimpregnated web is thus performed under temperature conditions leadingto a secondary vulcanization of the rubber impregnant. The dried,vulcanized sheet is pliant and mellow by reason of the plasticizing 56effect of the glycerine on the non-rubber solids, including resins andproteins, associated with the latex and by reason of the softeningaction of the glycerine on the cellulose fibers. Of the impregnatingmaterials added to theweb, which 00 may amount to about 60%, aboutone-fourth may be glycerine. In this connection, it is to be emphasizedthat the presence of glycerine in substantial amount in the base sheetof artificial leather is of decided advantage in that this means I thatthe migration of glycerine from the primary skin and surfacing filmssubsequently deposited on the sheet is minimized and accordingly thatthe stability of the finished product is enhanced. Before finishing thedried sheet of artificial [0 leather, the sheet is preferably moistenedand gently stretched while passing over heated, polished steel drums.The side of the sheet pressed against the smooth drum faces may then befinished as hereinbefore described. In some in- ;roils or by pressingbetween hot smooth plates in a hydraulic press, and to coat and finishthe smoothed sheet as above disclosed, the vulcaniis pulled apart as ina tensile strength tester, the skin and base sheet break practicallytogether.

nation of the rubber in the base sheet being completed during thepressing and/or tanning steps.

*The sheet may then again be pressed under a fine skiver plate wherebythe grain of natural leather is very closely simulated. It ischaracteristic of a sheet of interfelted, substantially unhydrated fiberto be of comparatively lumpy formation, so that proper smoothing isessential if minute surface blemishes are to be properly covered up witha relatively thin skin.

As a measure of the flexing resistance of our product we clampedspecimens in the testing machine shown in Figures 3 and 4 which creasesthem in much the way they are flexed across the vamp of the shoe in use.The testing machine is shown in Figures 3 and 4, wherein,-

Figure 3 is a front view of the machine.

Figure 4 is a section on the line 4-4 of Figure 3. The specimen I isclamped to the forms 2 and 3 and are held in place by the spring-steeltapes 4. The forms are roimded at the corners, the radius of curvaturebeing 8' inch. The form 2 is :fixed on the base 5; the form 3 is mountedin he guides O and is reciprocated by the eccentric I, the throw ofwhich is inch and which makes 350 R. P. M. The specimen is mounted withthe form 3 at its position furthest to the i right at which time thedistance between the nearest faces of the forms is inch. The tests wereconducted at 45% humidity and 70 F. It was found that specimens of upperstock, the skin of whichwould remain intact for 200 hours in the tester,would last about six weeks in actual use in the vamp of a woman's shoe;samples which held up 100 hours in the tester lasted only about 4 weeksin service.

It is characteristic of our product that it will fiex on the testingmachine without failure of the surface or of the base material for atleast 150 hours. In spite of the fact that it will undergo this severefiexing test, it will not peel off inlarge pieces if scuffed up andpicked at. It is also significant that when our artificial leather Wewish to have it understood that we are using the term fglue" in theforegoing description and in the appended claims in its comprehensivesense to include animal glue or equivalent water-dispersible,film-forming substance, no matter what the parent material for the gluemay be, for, it

is well known, that various proteinous or animal substances, such asfish, bones, blood albumen,

casein, or the like, may go into the preparation of water-soluble orwater-dispersibleglues. The

allies which we employ in the skin coat may, as

hereinbefore indicated, undergo a tanning treatment, although in thecase of soluble glues, like ammonium caseinate, a simple heating of theskin coat, forinstance, heating as hereinbefore described to atemperature of about 220 to 230 1". for about minutes or so, may sufilceto convert such glues to a relatively inert or waterinsoluble condition.I

We claim:

1. An artificial leather comprising a felted fibrous base impregnatedwith a rubber composl- 5 tion and provided with an elastic surfacing ofa weight ranging from about 6 to 18 grams per square foot, possessed ofbreathing qualities, capable of withstanding without impairment aflexing test of at least 150 hours, and having a 10 wet Or dry scuffresistance of at least about 4 minutes, said surfacing comprising tannedglue and being finished to simulate the finished skin side of naturalleather.

' 2. An artificial leather comprising a coated and impregnated feltedfibrous base, the coating and the base containing the same plasticizerso as to prevent migration of the plasticizer into the base withattendant embrittlement of the coating, said coating comprising tannedglue, being of a weight ranging from about 6 to 18 grams per squarefoot, and being finished to simulate the finished skin side of naturalleather.

3. An artificial leather comprising a rubberbonded base of interfeltedfibers coated with a tanned glue composition, the coating and the basecontaining the same plasticizer to inhibit migration of the plasticizerinto the base sheet, said coating being of a weight ranging from about 6to 18 grams per square foot and being finished to simulate the finishedskin side of natural leather.

4. An artificial leather comprising a felted fibrous base impregnatedwith a rubber composition and provided with a surfacing of a weightranging from about 6 to 18 grams per square foot, possessed of breathingqualities, capable of withstanding without impairment a flexing test ofat least 150 hours, and which when scufled up and picked at will breakoff in small pieces 40 rather than peel off in large portions, saidsurfacing comprising tanned glue, being of a weight ranging from about 6to 18 grams per square foot, and being finished to simulate the finishedskin side of natural leather.

5. An artificial leather comprising a rubberimpregnated felted fibrousbase carrying on a face thereof a skin including a primary coating ofrubber, glue, and glycerine, and a surface coating of tanned glue andglycerine, said skin being possessed of "breathing qualities, having aweight ranging from about 6 to 18 grams per square foot, and beingfinished to simulate the [finished skin side of natural leather.

- dried-out latex composition and carrying on a face thereof a skinincluding a primary coating ofrubber, glue, and glycerine, and asecondary coating of tanned glue and glycerine, said skin beingpossessed of "breathing qualities, having a weight ranging from about 6to 18 grams per square foot, and being finished to simulate the finishedskin side of natural leather.

7. An artificial leather comprising a felted fibrous base impregnatedwith a glycerinated, dried-out and vulcanized latex composition andcarrying on a face thereof a skin including a primary coating of rubber,glue, and glycerine, and a secondary coating of tanned glue andglycerine, said skin being possessed of breathing" qualities, having aweight ranging from about 6 to 18 grams per square foot, and beingfinished to simulate the finished skin side of natural leather.

8. An artificial leather comprising a rubbering comprising tanned glueand vulcanized rub--.

her and finished to simulate the finished skin side of natural leather,said coating being of a weight ranging from about 6 to 18 grams persquare foot, possessed-of breathing qualities, capable of withstandingwithout impairment a flexing test of at least hours, and having a wet ordry scuff resistance of at least about 4 minutes.

9. A method of finishing artificial leather comprising arubber-impregnated felted fibrous base, which comprises applying to thesurface of such leather a skin comprising a primary coat containinglatex, glue, and glycerine and a secondary coat containing glue andglycerine while restricting said skin to a thickness ranging from about6 to 18 grams per square foot, and tanning the glue content of saidcoats carried by said artificial leather.

10. A method of finishing artificial leather comprising arubber-impregnated. felted fibrous base, which comprises applying to thesurface of such leather a skin comprising a primary coat containinglatex, glue, 'and glycerine and a secondary coat containing glue andglycerine while restricting said skin to a thickness ranging from about6 to 18 grams persquare foot, and exposing said artificial leathercarrying said coats of'restricted thickness to the action of a gaseousatmosphere of tanning agent.

11. A method of finishing artificial leather comprising arubber-impregnated fibrous felted base, which comprises applying to thesurface of such leather a skin comprising a primary coat containinglatex, glue, and glycerine and a secondary coat containing glue andglycerine while restricting said skin to a thickness ranging from about6 to 18 grams per square foot, exposing said artificial leather carryingsaid coats of restricted thickness to the action of a gaseous atmosphereof tanning agent, and frictioning the surface coat until it acquires thedesired polish. 12. A method of finishing artificial leather comprisinga rubber-impregnated felted fibrous base, which comprises applying tothe surface of 5 such leather a skin comprising a primary coatcontaining latex, glue and glycerine and a secondary coat containingglue and glycerine while restricting said skin to a thickness rangingfrom about 6 to 18 grams per square foot, and exposing said coatedartificial leather to the action of formaldehyde vapor, thereby tanningthe glue content of said coats.

13. A method of finishing artificial leather comprising arubber-impregnated felted fibrous 15 base, which comprises applying tothe surface of such leather a skin comprising a primary coat containinglatex, glue, and glycerine and a secondary coat containing glue andglycerine while restricting said skin to a thickness ranging from 20about 6 to 18 grams per square foot, and exposing said coated artificialleather to the action of formaldehyde vapor, thereby tanning the gluecontent of said coats, at least part of said tanning reaction beingpromoted by elevated temperature. 25

14. A method of finishing artificial leather comprising arubber-impregnated felted fibrous base, which comprises applying to thesurface of such lea her a skin comprising a primary coat containinglatex, glue, and glycerine and a sec- 30 ondary coat containing glue andglycerine while restricting said skin to a thickness ranging from about6 to 18 grams per square foot, exposing said coated artificial leatherto the action of formaldehyde vapor at room temperature for aconsiderable period of time, thereby tanning the glue content of saidcoats, and then heating the artificial leather to complete the tanningreaction.

MILTON 0. serum. BENJAMIN G. HOOS;

